Coordinate measurement machine with distance meter used to establish frame of reference

ABSTRACT

A portable articulated arm coordinate measuring machine includes a distance meter to measure 3D coordinates of at least three targets to establish a position and orientation of the articulated arm within a frame of reference established by the at least three targets.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/524,028 filed Jun. 15, 2012, which is acontinuation-in-part of U.S. patent application Ser. No. 13/006,507filed Jan. 14, 2011, and claims the benefit of provisional applicationNo. 61/296,555 filed Jan. 20, 2010, provisional application No.61/355,279 filed Jun. 16, 2010, and provisional application No.61/351,347 filed on Jun. 4, 2010, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to a coordinate measuring machine, andmore particularly to a portable articulated arm coordinate measuringmachine having a connector on a probe end of the coordinate measuringmachine that allows accessory devices which use transit time of flightfor non-contact three dimensional measurement to be connected to thecoordinate measuring machine.

Portable articulated arm coordinate measuring machines (AACMMs) havefound widespread use in the manufacturing or production of parts wherethere is a need to rapidly and accurately verify the dimensions of thepart during various stages of the manufacturing or production (e.g.,machining) of the part. Portable AACMMs represent a vast improvementover known stationary or fixed, cost-intensive and relatively difficultto use measurement installations, particularly in the amount of time ittakes to perform dimensional measurements of relatively complex parts.Typically, a user of a portable AACMM simply guides a probe along thesurface of the part or object to be measured. The measurement data arethen recorded and provided to the user. In some cases, the data areprovided to the user in visual form, for example, three-dimensional(3-D) form on a computer screen. In other cases, the data are providedto the user in numeric form, for example when measuring the diameter ofa hole, the text “Diameter=1.0034” is displayed on a computer screen.

An example of a prior art portable articulated arm CMM is disclosed incommonly assigned U.S. Pat. No. 5,402,582 ('582), which is incorporatedherein by reference in its entirety. The '582 patent discloses a 3-Dmeasuring system comprised of a manually-operated articulated arm CMMhaving a support base on one end and a measurement probe at the otherend. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which isincorporated herein by reference in its entirety, discloses a similararticulated arm CMM. In the '147 patent, the articulated arm CMMincludes a number of features including an additional rotational axis atthe probe end, thereby providing for an arm with either a two-two-two ora two-two-three axis configuration (the latter case being a seven axisarm).

Three-dimensional surfaces may be measured using non-contact techniquesas well. One type of non-contact device, sometimes referred to as alaser line probe, emits a laser light either on a spot, or along a line.A imaging device, such as a charge-coupled device (CCD) for example, ispositioned adjacent the laser to capture an image of the reflected lightfrom the surface. The surface of the object being measured causes adiffuse reflection. The image on the sensor will change as the distancebetween the sensor and the surface changes. By knowing the relationshipbetween the imaging sensor and the laser and the position of the laserimage on the sensor, triangulation methods may be used to measure pointson the surface.

While existing CMM's are suitable for their intended purposes, what isneeded is a portable AACMM that has certain features of embodiments ofthe present invention.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a method a method isprovided for operating a portable articulated arm coordinate measuringmachine (AACMM) for measuring three-dimensional coordinates of an objectin space, the method including providing the AACMM in a AACMM frame ofreference having an origin, the AACMM having a manually positionable armportion, a base, a noncontact measurement device, and an electroniccircuit, the arm portion having an opposed first end and second end, thearm portion including a plurality of connected arm segments, each of theplurality of connected arm segments including at least one positiontransducer for producing a plurality of position signals, the first endconnected to the base, the noncontact measurement device connected tothe second end, an electromagnetic radiation transmitter, and a sensor,the electronic circuit configured to receive the plurality of positionsignals; providing a first reflective target at a first location havingfirst target three-dimensional coordinates in a target frame ofreference, a second reflective target at a second location having secondtarget three-dimensional coordinates in the target frame of reference,and a third reflective target at a third location having third targetthree-dimensional coordinates in the target frame of reference, whereinthe first location, the second location, and the third location arenon-collinear; manually positioning the second end to direct thetransmitted electromagnetic radiation to the first target; measuring afirst distance to the first target with the noncontact measurementdevice and measuring a first plurality of position signals; manuallypositioning the second end to direct the transmitted electromagneticradiation to the second target; measuring a second distance to thesecond target with the noncontact measurement device and measuring asecond plurality of position signals; manually positioning the secondend to direct the transmitted electromagnetic radiation to the thirdtarget; measuring a third distance to the third target with thenoncontact measurement device and measuring a third plurality ofposition signals; determining by a processor, relative to the targetframe of reference, first origin coordinates and first AACMM orientationangles, the first origin coordinates being three-dimensional coordinatesof the first origin in the target frame of reference and the first AACMMorientation angles being three rotational angles of orientation of thefirst AACMM in the target frame of reference, the first origincoordinates and the first AACMM orientation angles being based at leastin part on the first distance, the first plurality of signals, the firstthree-dimensional coordinates, the second distance, the second pluralityof signals, the second three-dimensional coordinates, the thirddistance, the third plurality of signals, and the thirdthree-dimensional coordinates; and storing the first origin coordinatesand the first AACMM orientation angles.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, exemplary embodiments are shown whichshould not be construed to be limiting regarding the entire scope of thedisclosure, and wherein the elements are numbered alike in severalFIGURES:

FIG. 1, including FIGS. 1A and 1B, are perspective views of a portablearticulated arm coordinate measuring machine (AACMM) having embodimentsof various aspects of the present invention therewithin;

FIG. 2, including FIGS. 2A-2D taken together, is a block diagram ofelectronics utilized as part of the AACMM of FIG. 1 in accordance withan embodiment;

FIG. 3, including FIGS. 3A and 3B taken together, is a block diagramdescribing detailed features of the electronic data processing system ofFIG. 2 in accordance with an embodiment;

FIG. 4 is an isometric view of the probe end of the AACMM of FIG. 1;

FIG. 5 is a side view of the probe end of FIG. 4 with the handle beingcoupled thereto;

FIG. 6 is a side view of the probe end of FIG. 4 with the handleattached;

FIG. 7 is an enlarged partial side view of the interface portion of theprobe end of FIG. 6;

FIG. 8 is another enlarged partial side view of the interface portion ofthe probe end of FIG. 5;

FIG. 9 is an isometric view partially in section of the handle of FIG.4;

FIG. 10 is an isometric view of the probe end of the AACMM of FIG. 1with a noncontact distance measurement device attached;

FIG. 11 is a schematic view of an embodiment wherein the device of FIG.10 is an interferometer system;

FIG. 12 is a schematic view of an embodiment wherein the device of FIG.10 is an absolute distance meter system;

FIG. 13 is a schematic view of an embodiment wherein the device of FIG.10 is a focusing type distance meter; and

FIG. 14 is a schematic view of an embodiment wherein the device of FIG.10 is a contrast focusing type of distance meter.

DETAILED DESCRIPTION

Portable articulated arm coordinate measuring machines (“AACMM”) areused in a variety of applications to obtain measurements of objects.Embodiments of the present invention provide advantages in allowing anoperator to easily and quickly couple accessory devices to a probe endof the AACMM that use structured light to provide for the non-contactmeasurement of a three-dimensional object. Embodiments of the presentinvention provide further advantages in providing for communicating datarepresenting a distance to an object measured by the accessory.Embodiments of the present invention provide still further advantages inproviding power and data communications to a removable accessory withouthaving external connections or wiring.

FIGS. 1A and 1B illustrate, in perspective, an AACMM 100 according tovarious embodiments of the present invention, an articulated arm beingone type of coordinate measuring machine. As shown in FIGS. 1A and 1B,the exemplary AACMM 100 may comprise a six or seven axis articulatedmeasurement device having a probe end 401 (FIG. 4) that includes ameasurement probe housing 102 coupled to an arm portion 104 of the AACMM100 at one end. The arm portion 104 comprises a first arm segment 106coupled to a second arm segment 108 by a first grouping of bearingcartridges 110 (e.g., two bearing cartridges). A second grouping ofbearing cartridges 112 (e.g., two bearing cartridges) couples the secondarm segment 108 to the measurement probe housing 102. A third groupingof bearing cartridges 114 (e.g., three bearing cartridges) couples thefirst arm segment 106 to a base 116 located at the other end of the armportion 104 of the AACMM 100. Each grouping of bearing cartridges 110,112, 114 provides for multiple axes of articulated movement. Also, theprobe end 401 may include a measurement probe housing 102 that comprisesthe shaft of an axis of rotation for the AACMM 100 (e.g., a cartridgecontaining an encoder system that determines movement of the measurementdevice, for example a probe 118, in an axis of rotation for the AACMM100). In this embodiment, the probe end 401 may rotate about an axisextending through the center of measurement probe housing 102. In use ofthe AACMM 100, the base 116 is typically affixed to a work surface.

Each bearing cartridge within each bearing cartridge grouping 110, 112,114 typically contains an encoder system (e.g., an optical angularencoder system). The encoder system (i.e., transducer) provides anindication of the position of the respective arm segments 106, 108 andcorresponding bearing cartridge groupings 110, 112, 114 that alltogether provide an indication of the position of the probe 118 withrespect to the base 116 (and, thus, the position of the object beingmeasured by the AACMM 100 in a certain frame of reference—for example alocal or global frame of reference). The arm segments 106, 108 may bemade from a suitably rigid material such as but not limited to a carboncomposite material for example. A portable AACMM 100 with six or sevenaxes of articulated movement (i.e., degrees of freedom) providesadvantages in allowing the operator to position the probe 118 in adesired location within a 360° area about the base 116 while providingan arm portion 104 that may be easily handled by the operator. However,it should be appreciated that the illustration of an arm portion 104having two arm segments 106, 108 is for exemplary purposes, and theclaimed invention should not be so limited. An AACMM 100 may have anynumber of arm segments coupled together by bearing cartridges (and,thus, more or less than six or seven axes of articulated movement ordegrees of freedom).

The probe 118 is detachably mounted to the measurement probe housing102, which is connected to bearing cartridge grouping 112. A handle 126is removable with respect to the measurement probe housing 102 by wayof, for example, a quick-connect interface. As will be discussed in moredetail below, the handle 126 may be replaced with another deviceconfigured to provide non-contact distance measurement of an object,thereby providing advantages in allowing the operator to make bothcontact and non-contact measurements with the same AACMM 100. Inexemplary embodiments, the probe 118 is a contacting measurement deviceand is removable. The probe 118 may have different tips 118 thatphysically contact the object to be measured, including, but not limitedto: ball, touch-sensitive, curved and extension type probes. In otherembodiments, the measurement is performed, for example, by anon-contacting device such as an interferometer or an absolute distancemeasurement (ADM) device. In an embodiment, the handle 126 is replacedwith the coded structured light scanner device using the quick-connectinterface. Other types of measurement devices may replace the removablehandle 126 to provide additional functionality. Examples of suchmeasurement devices include, but are not limited to, one or moreillumination lights, a temperature sensor, a thermal scanner, a bar codescanner, a projector, a paint sprayer, a camera, or the like, forexample.

As shown in FIGS. 1A and 1B, the AACMM 100 includes the removable handle126 that provides advantages in allowing accessories or functionality tobe changed without removing the measurement probe housing 102 from thebearing cartridge grouping 112. As discussed in more detail below withrespect to FIG. 2, the removable handle 126 may also include anelectrical connector that allows electrical power and data to beexchanged with the handle 126 and the corresponding electronics locatedin the probe end 401.

In various embodiments, each grouping of bearing cartridges 110, 112,114 allow the arm portion 104 of the AACMM 100 to move about multipleaxes of rotation. As mentioned, each bearing cartridge grouping 110,112, 114 includes corresponding encoder systems, such as optical angularencoders for example, that are each arranged coaxially with thecorresponding axis of rotation of, e.g., the arm segments 106, 108. Theoptical encoder system detects rotational (swivel) or transverse (hinge)movement of, e.g., each one of the arm segments 106, 108 about thecorresponding axis and transmits a signal to an electronic dataprocessing system within the AACMM 100 as described in more detailherein below. Each individual raw encoder count is sent separately tothe electronic data processing system as a signal where it is furtherprocessed into measurement data. No position calculator separate fromthe AACMM 100 itself (e.g., a serial box) is required, as disclosed incommonly assigned U.S. Pat. No. 5,402,582 ('582).

The base 116 may include an attachment device or mounting device 120.The mounting device 120 allows the AACMM 100 to be removably mounted toa desired location, such as an inspection table, a machining center, awall or the floor for example.

In one embodiment, the base 116 includes a handle portion 122 thatprovides a convenient location for the operator to hold the base 116 asthe AACMM 100 is being moved. In one embodiment, the base 116 furtherincludes a movable cover portion 124 that folds down to reveal a userinterface, such as a display screen.

In accordance with an embodiment, the base 116 of the portable AACMM 100contains or houses an electronic circuit having an electronic dataprocessing system that includes two primary components: a baseprocessing system that processes the data from the various encodersystems within the AACMM 100 as well as data representing other armparameters to support three-dimensional (3-D) positional calculations;and a user interface processing system that includes an on-boardoperating system, a touch screen display, and resident applicationsoftware that allows for relatively complete metrology functions to beimplemented within the AACMM 100 without the need for connection to anexternal computer.

The electronic data processing system in the base 116 may communicatewith the encoder systems, sensors, and other peripheral hardware locatedaway from the base 116 (e.g., a noncontact distance measurement devicethat can be mounted to the removable handle 126 on the AACMM 100). Theelectronics that support these peripheral hardware devices or featuresmay be located in each of the bearing cartridge groupings 110, 112, 114located within the portable AACMM 100.

FIG. 2 is a block diagram of electronics utilized in an AACMM 100 inaccordance with an embodiment. The embodiment shown in FIG. 2A includesan electronic data processing system 210 including a base processorboard 204 for implementing the base processing system, a user interfaceboard 202, a base power board 206 for providing power, a Bluetoothmodule 232, and a base tilt board 208. The user interface board 202includes a computer processor for executing application software toperform user interface, display, and other functions described herein.

As shown in FIG. 2A, the electronic data processing system 210 is incommunication with the aforementioned plurality of encoder systems viaone or more arm buses 218. In the embodiment depicted in FIG. 2B andFIG. 2C, each encoder system generates encoder data and includes: anencoder arm bus interface 214, an encoder digital signal processor (DSP)216, an encoder read head interface 234, and a temperature sensor 212.Other devices, such as strain sensors, may be attached to the arm bus218.

Also shown in FIG. 2D are probe end electronics 230 that are incommunication with the arm bus 218. The probe end electronics 230include a probe end DSP 228, a temperature sensor 212, a handle/deviceinterface bus 240 that connects with the handle 126 or the noncontactdistance measurement device 242 via the quick-connect interface in anembodiment, and a probe interface 226. The quick-connect interfaceallows access by the handle 126 to the data bus, control lines, andpower bus used by the noncontact distance measurement device 242 andother accessories. In an embodiment, the probe end electronics 230 arelocated in the measurement probe housing 102 on the AACMM 100. In anembodiment, the handle 126 may be removed from the quick-connectinterface and measurement may be performed by the noncontact distancemeasurement device 242 communicating with the probe end electronics 230of the AACMM 100 via the interface bus 240. In an embodiment, theelectronic data processing system 210 is located in the base 116 of theAACMM 100, the probe end electronics 230 are located in the measurementprobe housing 102 of the AACMM 100, and the encoder systems are locatedin the bearing cartridge groupings 110, 112, 114. The probe interface226 may connect with the probe end DSP 228 by any suitablecommunications protocol, including commercially-available products fromMaxim Integrated Products, Inc. that embody the 1-wire® communicationsprotocol 236.

FIG. 3A is a block diagram describing detailed features of theelectronic data processing system 210 of the AACMM 100 in accordancewith an embodiment. In an embodiment, the electronic data processingsystem 210 is located in the base 116 of the AACMM 100 and includes thebase processor board 204, the user interface board 202, a base powerboard 206, a Bluetooth module 232, and a base tilt module 208.

In an embodiment shown in FIG. 3A, the base processor board 204 includesthe various functional blocks illustrated therein. For example, a baseprocessor function 302 is utilized to support the collection ofmeasurement data from the AACMM 100 and receives raw arm data (e.g.,encoder system data) via the arm bus 218 and a bus control modulefunction 308. The memory function 304 stores programs and static armconfiguration data. The base processor board 204 also includes anexternal hardware option port function 310 for communicating with anyexternal hardware devices or accessories such as a noncontact distancemeasurement device 242. A real time clock (RTC) and log 306, a batterypack interface (IF) 316, and a diagnostic port 318 are also included inthe functionality in an embodiment of the base processor board 204depicted in FIG. 3.

The base processor board 204 also manages all the wired and wirelessdata communication with external (host computer) and internal (displayprocessor 202) devices. The base processor board 204 has the capabilityof communicating with an Ethernet network via an Ethernet function 320(e.g., using a clock synchronization standard such as Institute ofElectrical and Electronics Engineers (IEEE) 1588), with a wireless localarea network (WLAN) via a LAN function 322, and with Bluetooth module232 via a parallel to serial communications (PSC) function 314. The baseprocessor board 204 also includes a connection to a universal serial bus(USB) device 312.

The base processor board 204 transmits and collects raw measurement data(e.g., encoder system counts, temperature readings) for processing intomeasurement data without the need for any preprocessing, such asdisclosed in the serial box of the aforementioned '582 patent. The baseprocessor 204 sends the processed data to the display processor 328 onthe user interface board 202 via an RS485 interface (IF) 326. In anembodiment, the base processor 204 also sends the raw measurement datato an external computer.

Turning now to the user interface board 202 in FIG. 3B, the angle andpositional data received by the base processor is utilized byapplications executing on the display processor 328 to provide anautonomous metrology system within the AACMM 100. Applications may beexecuted on the display processor 328 to support functions such as, butnot limited to: measurement of features, guidance and training graphics,remote diagnostics, temperature corrections, control of variousoperational features, connection to various networks, and display ofmeasured objects. Along with the display processor 328 and a liquidcrystal display (LCD) 338 (e.g., a touch screen LCD) user interface, theuser interface board 202 includes several interface options including asecure digital (SD) card interface 330, a memory 332, a USB Hostinterface 334, a diagnostic port 336, a camera port 340, an audio/videointerface 342, a dial-up/cell modem 344 and a global positioning system(GPS) port 346.

The electronic data processing system 210 shown in FIG. 3A also includesa base power board 206 with an environmental recorder 362 for recordingenvironmental data. The base power board 206 also provides power to theelectronic data processing system 210 using an AC/DC converter 358 and abattery charger control 360. The base power board 206 communicates withthe base processor board 204 using inter-integrated circuit (I2C) serialsingle ended bus 354 as well as via a DMA serial peripheral interface(DSPI) 357. The base power board 206 is connected to a tilt sensor andradio frequency identification (RFID) module 208 via an input/output(I/O) expansion function 364 implemented in the base power board 206.

Though shown as separate components, in other embodiments all or asubset of the components may be physically located in differentlocations and/or functions combined in different manners than that shownin FIG. 3. For example, in one embodiment, the base processor board 204and the user interface board 202 are combined into one physical board.

Referring now to FIGS. 4-9, an exemplary embodiment of a probe end 401is illustrated having a measurement probe housing 102 with aquick-connect mechanical and electrical interface that allows removableand interchangeable device 400 to couple with AACMM 100. In theexemplary embodiment, the device 400 includes an enclosure 402 thatincludes a handle portion 404 that is sized and shaped to be held in anoperator's hand, such as in a pistol grip for example. The enclosure 402is a thin wall structure having a cavity 406 (FIG. 9). The cavity 406 issized and configured to receive a controller 408. The controller 408 maybe a digital circuit, having a microprocessor for example, or an analogcircuit. In one embodiment, the controller 408 is in asynchronousbidirectional communication with the electronic data processing system210 (FIGS. 2 and 3). The communication connection between the controller408 and the electronic data processing system 210 may be wired (e.g. viacontroller 420) or may be a direct or indirect wireless connection (e.g.Bluetooth or IEEE 802.11) or a combination of wired and wirelessconnections. In the exemplary embodiment, the enclosure 402 is formed intwo halves 410, 412, such as from an injection molded plastic materialfor example. The halves 410, 412 may be secured together by fasteners,such as screws 414 for example. In other embodiments, the enclosurehalves 410, 412 may be secured together by adhesives or ultrasonicwelding for example.

The handle portion 404 also includes buttons or actuators 416, 418 thatmay be manually activated by the operator. The actuators 416, 418 arecoupled to the controller 408 that transmits a signal to a controller420 within the probe housing 102. In the exemplary embodiments, theactuators 416, 418 perform the functions of actuators 422, 424 locatedon the probe housing 102 opposite the device 400. It should beappreciated that the device 400 may have additional switches, buttons orother actuators that may also be used to control the device 400, theAACMM 100 or vice versa. Also, the device 400 may include indicators,such as light emitting diodes (LEDs), sound generators, meters, displaysor gauges for example. In one embodiment, the device 400 may include adigital voice recorder that allows for synchronization of verbalcomments with a measured point. In yet another embodiment, the device400 includes a microphone that allows the operator to transmit voiceactivated commands to the electronic data processing system 210.

In one embodiment, the handle portion 404 may be configured to be usedwith either operator hand or for a particular hand (e.g. left handed orright handed). The handle portion 404 may also be configured tofacilitate operators with disabilities (e.g. operators with missingfinders or operators with prosthetic arms). Further, the handle portion404 may be removed and the probe housing 102 used by itself whenclearance space is limited. As discussed above, the probe end 401 mayalso comprise the shaft of an axis of rotation for AACMM 100.

The probe end 401 includes a mechanical and electrical interface 426having a first connector 429 (FIG. 8) on the device 400 that cooperateswith a second connector 428 on the probe housing 102. The connectors428, 429 may include electrical and mechanical features that allow forcoupling of the device 400 to the probe housing 102. In one embodiment,the interface 426 includes a first surface 430 having a mechanicalcoupler 432 and an electrical connector 434 thereon. The enclosure 402also includes a second surface 436 positioned adjacent to and offsetfrom the first surface 430. In the exemplary embodiment, the secondsurface 436 is a planar surface offset a distance of approximately 0.5inches from the first surface 430. This offset provides a clearance forthe operator's fingers when tightening or loosening a fastener such ascollar 438. The interface 426 provides for a relatively quick and secureelectronic connection between the device 400 and the probe housing 102without the need to align connector pins, and without the need forseparate cables or connectors.

The electrical connector 434 extends from the first surface 430 andincludes one or more connector pins 440 that are electrically coupled inasynchronous bidirectional communication with the electronic dataprocessing system 210 (FIGS. 2 and 3), such as via one or more arm buses218 for example. The bidirectional communication connection may be wired(e.g. via arm bus 218), wireless (e.g. Bluetooth or IEEE 802.11), or acombination of wired and wireless connections. In one embodiment, theelectrical connector 434 is electrically coupled to the controller 420.The controller 420 may be in asynchronous bidirectional communicationwith the electronic data processing system 210 such as via one or morearm buses 218 for example. The electrical connector 434 is positioned toprovide a relatively quick and secure electronic connection withelectrical connector 442 on probe housing 102. The electrical connectors434, 442 connect with each other when the device 400 is attached to theprobe housing 102. The electrical connectors 434, 442 may each comprisea metal encased connector housing that provides shielding fromelectromagnetic interference as well as protecting the connector pinsand assisting with pin alignment during the process of attaching thedevice 400 to the probe housing 102.

The mechanical coupler 432 provides relatively rigid mechanical couplingbetween the device 400 and the probe housing 102 to support relativelyprecise applications in which the location of the device 400 on the endof the arm portion 104 of the AACMM 100 preferably does not shift ormove. Any such movement may typically cause an undesirable degradationin the accuracy of the measurement result. These desired results areachieved using various structural features of the mechanical attachmentconfiguration portion of the quick connect mechanical and electronicinterface of an embodiment of the present invention.

In one embodiment, the mechanical coupler 432 includes a firstprojection 444 positioned on one end 448 (the leading edge or “front” ofthe device 400). The first projection 444 may include a keyed, notchedor ramped interface that forms a lip 446 that extends from the firstprojection 444. The lip 446 is sized to be received in a slot 450defined by a projection 452 extending from the probe housing 102 (FIG.8). It should be appreciated that the first projection 444 and the slot450 along with the collar 438 form a coupler arrangement such that whenthe lip 446 is positioned within the slot 450, the slot 450 may be usedto restrict both the longitudinal and lateral movement of the device 400when attached to the probe housing 102. As will be discussed in moredetail below, the rotation of the collar 438 may be used to secure thelip 446 within the slot 450.

Opposite the first projection 444, the mechanical coupler 432 mayinclude a second projection 454. The second projection 454 may have akeyed, notched-lip or ramped interface surface 456 (FIG. 5). The secondprojection 454 is positioned to engage a fastener associated with theprobe housing 102, such as collar 438 for example. As will be discussedin more detail below, the mechanical coupler 432 includes a raisedsurface projecting from surface 430 that adjacent to or disposed aboutthe electrical connector 434 which provides a pivot point for theinterface 426 (FIGS. 7 and 8). This serves as the third of three pointsof mechanical contact between the device 400 and the probe housing 102when the device 400 is attached thereto.

The probe housing 102 includes a collar 438 arranged co-axially on oneend. The collar 438 includes a threaded portion that is movable betweena first position (FIG. 5) and a second position (FIG. 7). By rotatingthe collar 438, the collar 438 may be used to secure or remove thedevice 400 without the need for external tools. Rotation of the collar438 moves the collar 438 along a relatively coarse, square-threadedcylinder 474. The use of such relatively large size, square-thread andcontoured surfaces allows for significant clamping force with minimalrotational torque. The coarse pitch of the threads of the cylinder 474further allows the collar 438 to be tightened or loosened with minimalrotation.

To couple the device 400 to the probe housing 102, the lip 446 isinserted into the slot 450 and the device is pivoted to rotate thesecond projection 454 toward surface 458 as indicated by arrow 464 (FIG.5). The collar 438 is rotated causing the collar 438 to move ortranslate in the direction indicated by arrow 462 into engagement withsurface 456. The movement of the collar 438 against the angled surface456 drives the mechanical coupler 432 against the raised surface 460.This assists in overcoming potential issues with distortion of theinterface or foreign objects on the surface of the interface that couldinterfere with the rigid seating of the device 400 to the probe housing102. The application of force by the collar 438 on the second projection454 causes the mechanical coupler 432 to move forward pressing the lip446 into a seat on the probe housing 102. As the collar 438 continues tobe tightened, the second projection 454 is pressed upward toward theprobe housing 102 applying pressure on a pivot point. This provides asee-saw type arrangement, applying pressure to the second projection454, the lip 446 and the center pivot point to reduce or eliminateshifting or rocking of the device 400. The pivot point presses directlyagainst the bottom on the probe housing 102 while the lip 446 is appliesa downward force on the end of probe housing 102. FIG. 5 includes arrows462, 464 to show the direction of movement of the device 400 and thecollar 438. FIG. 7 includes arrows 466, 468, 470 to show the directionof applied pressure within the interface 426 when the collar 438 istightened. It should be appreciated that the offset distance of thesurface 436 of device 400 provides a gap 472 between the collar 438 andthe surface 436 (FIG. 6). The gap 472 allows the operator to obtain afirmer grip on the collar 438 while reducing the risk of pinchingfingers as the collar 438 is rotated. In one embodiment, the probehousing 102 is of sufficient stiffness to reduce or prevent thedistortion when the collar 438 is tightened.

Embodiments of the interface 426 allow for the proper alignment of themechanical coupler 432 and electrical connector 434 and also protect theelectronics interface from applied stresses that may otherwise arise dueto the clamping action of the collar 438, the lip 446 and the surface456. This provides advantages in reducing or eliminating stress damageto circuit board 476 mounted electrical connectors 434, 442 that mayhave soldered terminals. Also, embodiments provide advantages over knownapproaches in that no tools are required for a user to connect ordisconnect the device 400 from the probe housing 102. This allows theoperator to manually connect and disconnect the device 400 from theprobe housing 102 with relative ease.

Due to the relatively large number of shielded electrical connectionspossible with the interface 426, a relatively large number of functionsmay be shared between the AACMM 100 and the device 400. For example,switches, buttons or other actuators located on the AACMM 100 may beused to control the device 400 or vice versa. Further, commands and datamay be transmitted from electronic data processing system 210 to thedevice 400. In one embodiment, the device 400 is a video camera thattransmits data of a recorded image to be stored in memory on the baseprocessor 204 or displayed on the display 328. In another embodiment thedevice 400 is an image projector that receives data from the electronicdata processing system 210. In addition, temperature sensors located ineither the AACMM 100 or the device 400 may be shared by the other. Itshould be appreciated that embodiments of the present invention provideadvantages in providing a flexible interface that allows a wide varietyof accessory devices 400 to be quickly, easily and reliably coupled tothe AACMM 100. Further, the capability of sharing functions between theAACMM 100 and the device 400 may allow a reduction in size, powerconsumption and complexity of the AACMM 100 by eliminating duplicity.

In one embodiment, the controller 408 may alter the operation orfunctionality of the probe end 401 of the AACMM 100. For example, thecontroller 408 may alter indicator lights on the probe housing 102 toeither emit a different color light, a different intensity of light, orturn on/off at different times when the device 400 is attached versuswhen the probe housing 102 is used by itself. In one embodiment, thedevice 400 includes a range finding sensor (not shown) that measures thedistance to an object. In this embodiment, the controller 408 may changeindicator lights on the probe housing 102 in order to provide anindication to the operator how far away the object is from the probe tip118. In another embodiment, the controller 408 may change the color ofthe indicator lights based on the quality of the image acquired by thecoded structured light scanner device. This provides advantages insimplifying the requirements of controller 420 and allows for upgradedor increased functionality through the addition of accessory devices.

Referring to FIGS. 10-14, a device 500 is shown that allows fornon-contact measurement of an object. In one embodiment, the device 500is removably coupled to the probe end 401 via the coupler mechanism andinterface 426. In another embodiment, the device 500 is integrallyconnected to the probe end 401. As will be discussed in more detailbelow, the device 500 may be an interferometer (FIG. 11) an absolutedistance measurement (ADM) device (FIG. 12), a focusing meter (FIG. 13and FIG. 14) or another type of non-contact distance measurement device.

The device 500 further includes an enclosure 501 with a handle portion510. In one embodiment, the device 500 may further include an interface426 on one end that mechanically and electrically couples the device 500to the probe housing 102 as described herein above. The interface 426provides advantages in allowing the device 500 to be coupled and removedfrom the AACMM 100 quickly and easily without requiring additionaltools. In other embodiments, the device 500 may be integrated into theprobe housing 102.

The device 500 includes an electromagnetic radiation transmitter, suchas a light source 502 that emits coherent or incoherent light, such as alaser light or white light for example. The light from light source 502is directed out of the device 500 towards an object to be measured. Thedevice 500 may include an optical assembly 504 and an optical receiver506. The optical assembly 504 may include one or more lenses, beamsplitters, dichromatic mirrors, quarter wave plates, polarizing opticsand the like. The optical assembly 504 splits the light emitted by thelight source and directs a portion towards an object, such as aretroreflector for example, and a portion towards the optical receiver506. The optical receiver 506 is configured receive reflected light andthe redirected light from the optical assembly 504 and convert the lightinto electrical signals. The light source 502 and optical receiver 506are both coupled to a controller 508. The controller 508 may include oneor more microprocessors, digital signal processors, memory and signalconditioning circuits.

Further, it should be appreciated that the device 500 is substantiallyfixed relative to the probe tip 118 so that forces on the handle portion510 do not influence the alignment of the device 500 relative to theprobe tip 118. In one embodiment, the device 500 may have an additionalactuator (not shown) that allows the operator to switch betweenacquiring data from the device 500 and the probe tip 118.

The device 500 may further include actuators 512, 514 which may bemanually activated by the operator to initiate operation and datacapture by the device 500. In one embodiment, the optical processing todetermine the distance to the object is performed by the controller 508and the distance data is transmitted to the electronic data processingsystem 210 via bus 240. In another embodiment optical data istransmitted to the electronic data processing system 210 and thedistance to the object is determined by the electronic data processingsystem 210. It should be appreciated that since the device 500 iscoupled to the AACMM 100, the electronic processing system 210 maydetermine the position and orientation of the device 500 (via signalsfrom the encoders) which when combined with the distance measurementallow the determination of the X, Y, Z coordinates of the objectrelative to the AACMM.

In one embodiment, the device 500 shown in FIG. 11 is an interferometer.An interferometer is a type of distance meter that sends a beam ofcoherent light, such as laser light for example, to a point on anobject. In the exemplary embodiment, the object is an externalretroreflector 516 for example. The interferometer combines the returnedlight with a reference beam of light to measure a change in distance ofan object. By arranging the retroreflector 516 at an initial positionwhere the distance D is known, as the retroreflector 516 is moved to anew position the distance D′ may be determined. With an ordinary orincremental interferometer, the distance is determined by countinghalf-wavelengths since the interference pattern of the light repeats forevery half wavelength of movement of the object point relative to thedistance meter. The retroreflector 516 may be a spherically mountedretroreflector that comprises a metal sphere into which a cube cornerretroreflector is embedded. The cube corner retroreflector comprisesthree perpendicular mirrors that come together at a common apex point.In an embodiment, the apex point is placed at the center of the metalsphere. By holding the sphere in contact with an object, the distance toobject surface points may be measured by the interferometer. Theretroreflector 516 may also be any other type of device that sends thelight back parallel to the outgoing light.

In an embodiment, the device 500 is an incremental interferometer. Theincremental interferometer has a measured distance D calculated usingD=a+(n+p)*(lambda/2)*c/n, where “a” is a constant, “n” is the integernumber of counts that have transpired in the movement of a target, “p”is the fractional part of a cycle (a number 0 to 1 corresponding to aphase angle of 0 to 360 degrees), “lambda” is the wavelength of thelight in vacuum, “c” is the speed of light in vacuum, and “n” is theindex of refraction of the air at wavelength of the light 524 at thetemperature, barometric pressure, and humidity of the air through whichthe light 524 passes. The index of refraction is defined as the speed oflight in vacuum divided by the speed of light in a local medium (in thiscase air), and so it follows that the calculated distance D depends onthe speed of light in air “c/n”. In an embodiment, light 518 from alight source 502 passes through a interferometer optic 504, travels to aremote retroreflector 516, passes through the interferometer optic 504in a return path, and enters an optical receiver. The optical receiveris attached to a phase interpolator. Together the optical receiver andphase interpolator include optics and electronics to decode the phase ofthe returning light and to keep track of the number of half-wavelengthcounts. Electronics within the phase interpolator or elsewhere withinthe articulated arm 100 or in an external computer determine theincremental distance moved by the retroreflector 516. The incrementaldistance traveled by the retroreflector 516 of FIG. 11 is D′−D. Adistance D′ at any given time may be determined by first finding theposition of the retroreflector at a reference position, which might forexample be a distance D from a reference point on the articulated armCMM. For example, if the retroreflector resides within a sphericallymounted retroreflector (SMR), a distance D′ may be found by firstlocating the retroreflector 516 at a reference location, which might befor example a magnetic nest configured to hold the SMR. Thereafter, aslong as the beam is not broken between the source of light 502 and theretroreflector 516, the total distance D′ can be determined by using areference distance as the value “a” in the equation discussedhereinabove. A reference distance might be determined, for example, bymeasuring a reference sphere with the scanner held at a variety oforientations. By self-consistently solving for the coordinates of thereference sphere, the reference distance can be determined.

FIG. 11 shows an emitted outgoing beam of light 524 travelling parallelto, but offset from, the returning beam of light 524B. In some cases, itmay be preferable to have the light return on itself so that the light524 and 524B are traveling along the same path but in oppositedirections. In this case, it may be important to use an isolation methodto keep reflected light from entering and destabilizing the light source520. One means for isolating the laser from the returning light is toplace a Faraday isolator in the optical pathway between the light source502 and the returning light 524B.

In one embodiment of an incremental interferometer, the interferometeris a homodyne type of the device such that the light source 502 is alaser that operates on a single frequency. In other embodiments, thedevice may be a heterodyne type of device and the laser operates on atleast two frequencies to produce two overlapping beams that arepolarized and orthogonal. The light source 502 emits a light 518 that isdirected into a beam splitting device 520. Here, a first portion 522 ofthe light is reflected and transmitted to the optical receiver 506. Thefirst portion 522 is reflected off of at least one mirror 523 to directthe first portion to the optical receiver 506. In the exemplaryembodiment, the first portion 522 is reflected off a plurality ofmirrors 523 and the beam splitter 520. This first portion 522 is areference beam of light that used for comparison with a returned orreflected light.

A second portion 524 of the light is transmitted through the beamsplitting device 520 and is directed towards the retroreflector 516. Itshould be appreciated that the optical assembly 504 may further includeother optical components, such as but not limited to lenses, quarterwave plates, filters and the like (not shown) for example. The secondportion 524 of light travels to the retroreflector 516, which reflectsthe second portion 524 back towards the device 500 along a path 527 thatis parallel to the outgoing light. The reflected light is received backthrough the optical assembly where it is transmitted through the beamsplitting device 520 to the optical receiver 506. In the exemplaryembodiment, as the returning light is transmitted through the beamsplitting device 520, it joins a common optical path with the light offirst portion 522 to the optical receiver 502. It should be appreciatedthat the optical assembly 504 may further include additional opticalcomponents (not shown), such as an optic that produces a rotating planeof polarization for example, between the beam splitting device 520 andthe optical receiver 506. In these embodiments, the optical receiver 506may be composed of multiple polarization sensitive receivers that allowfor power normalization functionality.

The optical receiver 506 receives both the first portion 522 and thesecond portion 524 light. Since the two light portions 522, 524 eachhave a different optical path length, the second portion 524 will have aphase shift when compared to the first portion 522 at the opticalreceiver 506. In an embodiment where the device 500 is a homodyneinterferometer, the optical receiver 506 generates an electrical signalbased on the change in intensity of the two portions of light 522, 524.In an embodiment where the device 500 is a heterodyne interferometer,the receiver 506 may allow for phase or frequency measurement using atechnique such as a Doppler shifted signal for example. In someembodiments, the optical receiver 506 may be a fiber optic pickup thattransfers the received light to a phase interpolator 508 or spectrumanalyzer for example. In still other embodiments, the optical receiver506 generates an electrical signal and transmits the signal to a phaseinterpolator 508.

In an incremental interferometer, it is necessary to keep track of thechange in the number of counts n (from the equation describedhereinabove). For the case of which the beam of light is kept on aretroreflector 516, the optics and electronics within the opticalreceiver 506 may be used to keep track of counts. In another embodiment,another type of measurement is used, in which the light from thedistance meter is sent directly onto the object to be measured. Theobject, which might be metallic, for example, may reflect lightdiffusely so that only a relatively small fraction of the light returnsto an optical receiver. In this embodiment, the light returns directlyon itself so that the returning light is substantially coincident withthe outgoing light. As a result, it may be necessary to provide a meansto reduce the amount of light feeding back into the light source 502,such as with a Faraday isolator for example.

One of the difficulties in measuring the distance to a diffuse target isthat it is not possible to count fringes. In the case of aretroreflector target 516, it is known that the phase of the lightchanges continuously as the retroreflector is moved away from thetracker. However, if a beam of light is moved over an object, the phaseof the returning light may change discontinuously, for example, when thelight passes by an edge. In this instance, it may be desired to use atype of interferometer known as an absolute interferometer. An absoluteinterferometer simultaneously emits multiple wavelengths of light, thewavelengths configured to create a “synthetic wavelength,” which mightbe on the order of a millimeter, for example. An absolute interferometerhas the same accuracy as an incremental interferometer except that it isnot necessary to count fringes for each half wavelength of movement.Measurements can be made anywhere within a region corresponding to onesynthetic wavelength.

In an embodiment, the optical assembly 504 may include a steering mirror(not shown), such as a micro-electromechanical system (MEMS) mirror thatallows light from an absolute interferometer to be reflected from thescanner and received back by the scanner to measure rapidly over anarea.

In one embodiment the device may include an optional image acquisitiondevice, such as a camera 529, which is used in combination with anabsolute interferometer. The camera 529 includes a lens and aphotosensitive array. The lens is configured to image the illuminatedobject point on a photosensitive array. The photosensitive array isconfigured to be responsive to the wavelengths of light emitted by theabsolute interferometer. By noting the position of the imaged light onthe photosensitive array, it is possible to determine the ambiguityrange of the object point. For example, suppose that an absoluteinterferometer has an ambiguity range of 1 mm. Then as long as thedistance to the target is known to within one millimeter, there is noproblem in using the interferometer to find the distance to the target.However, suppose that the distance to the target is not known to withinthe ambiguity range of one millimeter. In one embodiment, a way to findthe distance to the target to within the ambiguity range is to place thecamera 529 near the point of emission of the beam of light. The cameraforms an image of the scattered light on the photosensitive array. Theposition of the imaged spot of light depends on the distance to theoptical target and thereby provides a way of determining the distance tothe target to within the ambiguity range.

In an embodiment, the distance measurement device uses coherent light(e.g. a laser) in the determination of the distance to the object. Inone embodiment, the device varies the wavelength of a laser as afunction of time, for example, linearly as a function of time. Some ofthe outgoing laser beam is sent to an optical detector and another partof the outgoing laser beam that travels to the retroreflector is alsosent to the detector. The optical beams are mixed optically in thedetector and an electrical circuit evaluates the signal from the opticaldetector to determine the distance from the distance meter to theretroreflector target.

In one embodiment the device 500 is an absolute distance meter (ADM)device. An ADM device typically uses an incoherent light and determinesa distance to an object based on the time required to travel from thedistance meter to the target and back. Although ADM devices usually havelower accuracy than interferometers, an ADM provides an advantage indirectly measuring distance to an object rather than measuring a changein distance to the object. Thus, unlike an interferometer, an ADM doesnot require a known initial position.

One type of ADM is a pulsed time-of-flight (TOF) ADM. With a pulsed TOFADM, a laser emits a pulse of light. Part of the light is sent to anobject, scatters off the object, and is picked up by an optical detectorthat converts the optical signal into an electrical signal. Another partof the light is sent directly to the detector (or a separate detector),where it is converted into an electrical signal. The time dt between theleading edge of the two electrical pulse signals is used to determinethe distance to from the distance meter to the object point. Thedistance D is just D=a+dt*c/(2n), where a is a constant, c is the speedof light in vacuum, and n is the index of refraction of light in air.

Another type of ADM is a phase-based ADM. A phased-based ADM is one inwhich a sinusoidal modulation is directly applied to a laser to modulatethe optical power of the emitted laser beam. The modulation is appliedas either a sinusoid or a rectangle. The phase associated with thefundamental frequency of the detected waveform is extracted. Thefundamental frequency is the main or lowest frequency of the waveform.Typically, the phase associated with the fundamental frequency isobtained by sending the light to an optical detector to obtain anelectrical signal, condition the light (which might include sending thelight through amplifiers, mixer, and filters), converting the electricalsignals into digitized samples using an analog-to-digital converter, andthen calculating the phase using a computational method.

The phase-based ADM has a measured distance D equal toD=a+(n+p)*c/(2*f*n), where “a” is a constant, “n” and “p” are integerand fractional parts of the “ambiguity range” of an object point, and“f” is the frequency of modulation, “c” is the speed of light in vacuum,and n is the index of refraction. The quantity R=c/(2*f*n) is theambiguity range. If, for example, the modulation frequency is f=3 GHz,then from the formula the ambiguity range is approximately 50 mm. Theformula for “D” shows that calculated distance depends on the speed oflight in air, “c/n”. As in the case of the absolute interferometer, oneof the parameters that it is desirable to determine is the ambiguityrange for the object point under investigation. For an AACMM 100 used tomeasure the coordinates of a diffuse surface, the beam of light from thedevice 500 may in the course of a few milliseconds be directed toobjects separated by several meters. If the ambiguity range was notdetermined, such a large change would likely exceed the ambiguity rangeof the device and hence would leave the ADM without knowledge of thedistance to the object point.

In one embodiment the emitted light is modulated at a plurality offrequencies so that the ambiguity range may be determined in real time.For example, in one embodiment four different modulation frequencies maybe simultaneously applied to laser light. By known means of sampling andextraction procedures, the absolute distance to the target can bedetermined by calculating the phase for each of these four frequencies.In other embodiments, fewer than four frequencies are used. Phase-basedADMs may be used at either near or far ranges. Modulation and processingmethods are possible with other types of incoherent distance meters.Such distance meters are well known in the art and are not discussedfurther.

In one embodiment shown in FIG. 12, the device 500 is an ADM device thatincludes a light source 528, an isolator 530, ADM electronics 546, afiber network 536, a fiber launch 538, and optionally a beam splitter540 and position detector 542. The light source 528 may be laser such asa red or infrared laser diode for example. Laser light may be sentthrough an isolator 530, which may be a Faraday isolator or anattenuator, for example. The isolator 530 may be fiber coupled at itsinput and output ports. ADM electronics 532 modulates the light source528 by applying a radio frequency (RF) electrical signal to an input ofthe laser. In an embodiment, the RF signal is applied through the cable532 which sinusoidally modulates the optical power of the light emittedby the laser at one or more modulation frequencies. The modulated lightpassing through the isolator travels to the fiber network 536. Some ofthe light travels over optical fiber 548 to the reference channel of theADM electronics 546. Another portion of the light travels out of thedevice 500, reflects off target 516, and returns to the device 500. Inone embodiment, the target 516 is a non-cooperative target such as adiffusely reflecting material such as aluminum or steel. In anotherembodiment, the target 516 is a cooperative target, such as aretroreflector target, for example, that returns most of the light backto the device 500. Light entering the device 500 passes back through thefiber launch 538 and fiber network 536 and enters the measure channel ofthe ADM electronics 546 through the fiber optic cable 550. The ADMelectronics 546 includes optical detectors that convert the referenceand measure optical signals received from the optical fiber 548 and 550into electrical reference and measure signals. These signals areprocessed with electronics to determine a distance to the target.

In one embodiment, the light from the device 500 is sent to aretroreflector rather than a non-cooperative (diffusely scattering)target. In this case, a position detector 542 may be included to receivea small amount of light reflected off a beamsplitter 540. The signalreceived by the position detector 542 may be used by a control system tocause the light beam from the device 500 to track a movingretroreflector 516. If a scattering target is used rather than aretroreflective target, the beamsplitter 540 and the position detector542 may be omitted.

In one embodiment, the ADM device 500 incorporates a configuration suchas that described in commonly owned U.S. Pat. No. 7,701,559 which isincorporated herein by reference. It should be appreciated that both theinterferometer devices and the ADM devices determine the distance to theobject at least in part based on the speed of light in air.

Another type of distance meter is one based on a focusing method.Examples of focusing distance meters are a chromatic focusing meter, acontrast focusing meter, and an array sensing focusing meter. A deviceusing a chromatic focusing method such as the one shown in FIG. 13,incoherent white light is generated by the light source 552. Due to achromatic aberration of a lens 554 in the optical assembly the light isfocused in a “focal line” on the object 556 based on the wavelength oflight. As a result, different wavelengths components of the white lightare focused at different distances. Using a spectrometer 557, thedistance to the object 556 may be determined.

Another type of focusing distance meter shown in FIG. 14 is a contrastfocusing device. In this embodiment, the distance to the object isdetermined by focusing to a maximum contrast or image sharpness. Thefocusing is achieved by moving a camera 558 along an axis in thedirection of the object 560. When the position of greatest contrast hasbeen found, the object 560 lies on the optical axis of the sensor 562 ata known distance. This known distance is predetermined during acalibration process.

In one embodiment, the device 500 may be an array sensing focusingmeter. In this type of device, a source of light sends light through alens and a beam splitter. Part of the light strikes the object, reflectsoff the beam splitter, and travels to a photosensitive array. If theobject under inspection is at the focal position of the spot of light,the light on the photosensitive array will be very small. Hence theAACMM 100 could be used to capture the 3D coordinates whenever the spoton the array was sufficiently small.

In still another embodiment, the device 500 may be a conoscopicholography device. In this type of device, the surface of the object isprobed by a laser point. The laser light is diffusely reflected by thesurface to form a point light source. The light cone emanating from thispoint is widened by an optical system. A birefringent crystal isarranged between two circular polarizers to split the light into anordinary beam and an extraordinary beam. After transmitting through thesecond polarizing lens, the two beams superimpose to generate aholographic fringe pattern that may be acquired by a photosensitivesensor, such as a CCD camera. The distance to the object is determinedfrom the interference fringes by image processing.

It should be appreciated that while the focusing devices and theconoscopic holography devices may depend on the index of refraction oflight in air, the determination of distance for these devices isindependent of the speed of light in air.

The reach of an AACMM is often relatively short in comparison to theenvironment in which it is located. For example, an articulated arm maybe used to measure large tooling structures for an aircraft, the toolingstructures being located within a large hangar or manufacturingfacility. In such situations, it is often necessary to move the AACMMfrom one location to another while measuring the same component. Forexample, for the large tooling structure described above, it may benecessary to move the AACMM from a left side of the tooling structure toa middle part of the structure and to provide the three-dimensionalcoordinates measured by the AACMM within a common frame of reference. Inthe past, various methods have been established for doing this, andalthough these methods have been generally suitable for their intendedpurpose, they have not satisfied the need for doing this while movingthe AACMM over large distances.

In an embodiment, a distance meter is attached to the end of the AACMM.The AACMM has an origin having three translational degrees of freedom.The AACMM also has an orientation, which has three orientational degreesof freedom. The AACMM is located within an environment having its ownframe of reference, referred to herein as a target frame of reference.For example, in the example given above, the large tooling structure maybe described by a CAD model or by a model obtained from prior 3Dmeasurements. In relation to the CAD model or measured model, the targetframe of reference is assigned. The target frame of reference has atarget origin, usually assigned Cartesian coordinates (0,0,0) within thetarget frame of reference. The target frame of reference will also havean orientation, which may be described in terms of three Cartesian axesx, y, and z.

The AACMM has an AACMM origin and an AACMM orientation in relation tothe target frame of reference. In other words, the AACMM origin isoffset from the target frame of reference by some amount dx, dy, dz, andthe three axes of the AACMM frame of reference may be described by threerotation angles relative to the axes of the target frame of reference.

It is often desirable to know the AACMM frame of reference within thetarget frame of reference, for example, when trying to compare measuredvalues to those indicated in a CAD model. By such means, the AACMM maydetermine whether a component or tool has been manufactured withinspecified tolerances. For the case in which the AACMM is moved from afirst AACMM frame of reference to a second AACMM frame of reference, itis useful to know both the first and second AACMM frame of reference inthe target frame of reference.

A distance meter attached to the end of the AACMM may be used to providethe mathematical transformations needed to move from one frame toanother. To do this, the distance meter measures the distance to atleast three targets having 3D coordinates known at least approximatelywithin the target frame of reference. In some cases, the locations ofthe at least three targets are arbitrary and are not known evenapproximately. In some cases, a CAD model shows nominal 3D coordinatesof features on an object. By measuring 3D coordinates of at least threefeatures, the arm may construct x, y, and z (or equivalent) axes for atarget coordinate system. For example, a first measured point mayestablish the origin. A second measured point may be used to establishthe x axis in the target frame of reference. The third measured pointmay be used to establish the y and z axes. (The y axis is perpendicularto the x axis, and the z axis is perpendicular to both the x and yaxes.) In other cases, a large number of points may be measured with thearm, and a best fit procedure used to determine a best fit to a CADmodel. This best fit then provides a basis for the target frame ofreference.

Regardless of the method used, by measuring with the AACMM the 3Dcoordinates of at least three points, the arm may determine the positionand orientation of the AACMM frame of reference in the target frame ofreference. In some cases, this may be done over a region extendingbeyond an individual tool or component and may extend to an entirebuilding. For example, a building might have multiple targets measuredby distance meters to establish a frame of reference for all objectswithin the building.

The operation of moving an articulated arm is moved to more than oneposition is referred to as relocation, and the method of establishing acommon frame of reference following relocation is often referred to asregistration.

In an embodiment, at least three targets are provided within the targetframe of reference. These targets may be cooperative or non-cooperativetargets. An example of a cooperative target is a retroreflector—forexample, a cube corner retroreflector. An example of a non-cooperativetarget is a feature on an object—for example, a sphere or a hole. Anexample of a target that may be considered cooperative ornon-cooperative is a highly reflective target, for example, a highlyreflective circular target. Such targets are often referred to asretroreflective targets even though they do not reflect as much light asa cube corner retroreflector, for example. In some cases,non-cooperative targets are natural features of an object—for example,the point of intersection of three planar surfaces.

While the invention has been described with reference to exampleembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

What is claimed is:
 1. A method of operating a portable articulated armcoordinate measuring machine (AACMM) for measuring three-dimensionalcoordinates of an object in space, comprising: providing the AACMM in aAACMM frame of reference having an origin, the AACMM having a manuallypositionable arm portion, a base, a noncontact measurement device, andan electronic circuit, the arm portion having an opposed first end andsecond end, the arm portion including a plurality of connected armsegments, each of the plurality of connected arm segments including atleast one position transducer for producing a plurality of positionsignals, the first end connected to the base, the noncontact measurementdevice connected to the second end, an electromagnetic radiationtransmitter, and a sensor, the electronic circuit configured to receivethe plurality of position signals; providing a first reflective targetat a first location having first target three-dimensional coordinates ina target frame of reference, a second reflective target at a secondlocation having second target three-dimensional coordinates in thetarget frame of reference, and a third reflective target at a thirdlocation having third target three-dimensional coordinates in the targetframe of reference, wherein the first location, the second location, andthe third location are non-collinear; manually positioning the secondend to direct the transmitted electromagnetic radiation to the firsttarget; measuring a first distance to the first target with thenoncontact measurement device and measuring a first plurality ofposition signals; manually positioning the second end to direct thetransmitted electromagnetic radiation to the second target; measuring asecond distance to the second target with the noncontact measurementdevice and measuring a second plurality of position signals; manuallypositioning the second end to direct the transmitted electromagneticradiation to the third target; measuring a third distance to the thirdtarget with the noncontact measurement device and measuring a thirdplurality of position signals; determining by a processor, relative tothe target frame of reference, first origin coordinates and first AACMMorientation angles, the first origin coordinates being three-dimensionalcoordinates of the first origin in the target frame of reference and thefirst AACMM orientation angles being three rotational angles oforientation of the first AACMM in the target frame of reference, thefirst origin coordinates and the first AACMM orientation angles beingbased at least in part on the first distance, the first plurality ofsignals, the first three-dimensional coordinates, the second distance,the second plurality of signals, the second three-dimensionalcoordinates, the third distance, the third plurality of signals, and thethird three-dimensional coordinates; and storing the first origincoordinates and the first AACMM orientation angles.
 2. The method ofclaim 1 wherein, in the step of providing a first reflective target, thefirst reflective target is a retroreflector.
 3. The method of claim 1wherein, in the step of providing a first reflective target, the firstreflective target is a non-cooperative target.
 4. The method of claim 1wherein, in the step of providing the AACMM, the AACMM has a contactmeasurement device connected to the second end and the electroniccircuit is further configured to determine a position of the contactmeasurement device.
 5. The method of claim 4 wherein, in the step ofproviding the AACMM, the contact measurement device is a probe tip. 6.The method of claim 4, further comprising: touching the contactmeasurement device to a feature of the object; and measuring fourththree-dimensional coordinates of the feature in the target frame ofreference, the fourth three-dimensional coordinates based at least inpart on the determined position of the contact measurement device, thedetermined first origin coordinates, and the determined first AACMMorientation angles.
 7. The method of claim 1, further comprising:manually positioning the second end to direct the transmittedelectromagnetic radiation to a fourth reflective target; measuring afourth distance to the fourth reflective target with the noncontactmeasurement device and measuring a fourth plurality of position signals;and determining by the processor, relative to the target frame ofreference, three-dimensional coordinates of the fourth reflectivetarget, based at least in part on the measured fourth distance, themeasured fourth plurality of position signals, the determined firstorigin coordinates, and the determined first AACMM orientation angles.8. The method of claim 1, further comprising: moving the AACMM, relativeto the target frame of reference, to second origin coordinates andsecond AACMM orientation angles, manually positioning the second end todirect the transmitted electromagnetic radiation to the first target;measuring a fourth distance to the first target with the noncontactmeasurement device and measuring a fourth plurality of position signals;manually positioning the second end to direct the transmittedelectromagnetic radiation to the second target; measuring a fifthdistance to the second target with the noncontact measurement device andmeasuring a fifth plurality of position signals; manually positioningthe second end to direct the transmitted electromagnetic radiation tothe third target; measuring a sixth distance to the third target withthe noncontact measurement device and measuring a sixth plurality ofposition signals; determining by the processor, relative to the targetframe of reference, second origin coordinates and second AACMMorientation angles, the second origin coordinates beingthree-dimensional coordinates of the origin in the target frame ofreference and the second AACMM orientation angles being three rotationalangles of orientation of the AACMM in the target frame of reference, thesecond origin coordinates and the second AACMM orientation angles beingbased at least in part on the fourth distance, the fourth plurality ofsignals, the first three-dimensional coordinates, the fifth distance,the fifth plurality of signals, the second three-dimensionalcoordinates, the sixth distance, the sixth plurality of signals, and thethird three-dimensional coordinates; and storing the second origincoordinates and the second AACMM orientation angles.